Hollerith constant
Fortran data structure
Hollerith constants, named in honor of Herman Hollerith, were used in early FORTRAN programs to allow manipulation of character data.
Early FORTRAN had no CHARACTER data type, only numeric types. In order to perform character manipulation, characters needed to be placed into numeric variables using Hollerith constants. For example, the constant 3HABC specified a three-character string "ABC", identified by the initial integer representing the string length 3 and the specified Hollerith character H, followed by the string data ABC. These constants were typeless, so that there were no type conversion issues. If the constant specified fewer characters than was possible to hold in a data item, the characters were then stored in the item left-justified and blank-filled.
Mechanics
By the FORTRAN 66 Standard, Hollerith syntax was allowed in the following uses:
As constants in DATA statements
As constant actual arguments in subroutine CALL statements
As edit descriptors in FORMAT statements
Portability was problematic with Hollerith constants. First, word sizes varied on different computer systems, so the number of characters that could be placed in each data item likewise varied. Implementations varied from as few as two to as many as ten characters per word. Second, it was difficult to manipulate individual characters within a word in a portable fashion. This led to a great deal of shifting and masking code using non-standard, vendor-specific, features.
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